Aerospace mechanical structures encounter various forms of damage throughout their operation due to mechanical stimuli. Structural health monitoring (SHM) is suggested as a way to actively check the integrity of a component by using a system of sensors. However, these conventional sensors can often require external power that is not always readily available in aerospace, thus the development of self-powered sensors could prove beneficial for SHM applications. In this study, the design of multifunctional mechano-luminescent-optoelectronic (MLO) composites strain sensor is suggested. The MLO composites sensor is composed of two transformative materials: 1) mechano-luminescent (ML) copper-doped zinc sulfide (ZnS:Cu) and 2) mechano-optoelectronic (MO) poly(3-hexylthiophene) (P3HT). ML ZnS:Cu emits light in response to mechanical stimuli. MO P3HT showed self-sensing capability by generating direct current (DC) sensor signal under light. First, ZnS:Cu ML crystals will be embedded in polydimethylsiloxane (PDMS) matrix to fabricate ZnS:Cu/PDMS elastomeric composites. ML light emission characteristics of ZnS:Cu/PDMS will be studied by subjecting the ZnS:Cu/PDMS to cyclic tensile strain loadings while videos are recorded of the light emission. The data are analyzed using a statistical factorial methodology so that a regression model to predict light emission based on loading strain and frequency can be calculated. Second, MO P3HT-based self-sensing thin films will be fabricated on glass slides using a spin-coating technique. Last, self-powered sensing capability of the MLO composites strain sensor will be validated by measuring DC voltage (DCV) in close proximity of the ZnS:Cu/PDMS subjected to cyclic tensile loadings.
A resonant cavity method is presented which can measure loss tangents and dielectric constants for materials with dielectric constant from 150 to 10 000 and above. This practical and accurate technique is demonstrated by measuring barium strontium zirconium titanate bulk ferroelectric ceramic blocks. Above the Curie temperature, in the paraelectric state, barium strontium zirconium titanate has a sufficiently low loss that a series of resonant modes are supported in the cavity. At each mode frequency, the dielectric constant and loss tangent are obtained. The results are consistent with low frequency measurements and computer simulations. A quick method of analyzing the raw data using the 2D static electromagnetic modeling code SuperFish and an estimate of uncertainties are presented.
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